Quantum Optics Seminar by Gregor Weihs
Creation and interference of multiphoton states
Quantum states of multiple photons are conjectured to enable all-optical quantum repeaters and quantum computers. While photon loss is ubiquitous and source and detection efficiencies are from perfect, there are models that can deal with these errors with reasonable overhead and the advantage that stochastic noise is very small in typical circuit implementations.
In our work on efficient semiconductor sources of multiphoton states we employ several types of quantum dots to create entangled photon pairs and photon triplets. Sophisticated growth and control techniques boost the efficiency and quality of the emitted quantum states. For example, with two-photon coherent excitation, we achieve high-quality time-bin entanglement  and nanowires act as antennas to guide multiple photons from a quantum dot molecule  to a collection lens.
Applying multiphoton states in any linear optical network involves multiparticle interference. Our theoretical results on the complete generalization of the Hong-Ou-Mandel interference covers all possible scenarios of an arbitrary number of bosons or fermions in an arbitrary multiport beamsplitter with a surprisingly simple criterion . In a slightly different setting, we experimentally investigated the interference of a time-correlated three-photon state through Franson interferometry . I will show how we achieved genuine three-photon interference with high visibility, which enables tests of the foundations of quantum mechanics.
 H. Jayakumar, A. Predojević, T. Kauten, T. Huber, G. S. Solomon, and G. Weihs, Time-bin entangled photons from a quantum dot, Nature Commun. 5, 4251 (2014).
 M. Khoshnegar, T. Huber, A. Predojević, D. Dalacu, M. Prilmüller, et al., A solid state source of photon triplets based on quantum dot molecules, Nature Commun. 8, 15716 (2017).
 C. Dittel, G. Dufour, M. Walschaers, G. Weihs, A. Buchleitner, and R. Keil, Totally Destructive Many-Particle Interference, Phys. Rev. Lett. 120, 240404 (2018).
 S. Agne, T. Kauten, J. Jin, E. Meyer-Scott, J. Z. Salvail, et al., Observation of Genuine Three-Photon Interference, Phys. Rev. Lett. 118, 153602 (2017).